1. Field of the Invention
The present invention relates to a process for the production of 1-amino-1-methyl-3(4)-aminomethylcyclohexane (AMCA), the precursor for the production of 1-isocyanato-1-methyl-3(4)-isocyanatomethylcyclo-hexane (IMCI).
2. Description of the Prior Art
DE-A 4,401,929 describes a process for the preparation of 1-amino-1-methyl-3(4)-aminomethyl cyclohexane (AMCA) that may be illustrated by the following reaction scheme: ##STR1##
According to the reaction mechanism, 4(5)-cyano-1-methyl cyclohexene (CMC) is reacted with hydrocyanic acid in the presence of sulphuric acid to give 1-formamido-1-methyl-3(4)-cyano cyclohexane (FMC), which can be extracted from the acidic aqueous phase with suitable water-immiscible solvents after excess hydrocyanic acid has been removed by distillation and the reaction mixture has been diluted with water. Another known variant (see DE-A 4,401,929) for isolating FMC from the aqueous reaction mixture, which arises in accordance with the Ritter reaction, is to neutralize the latter acid mixture with ammonia, optionally after diluting with water, such that the mixture contains about 20 to 70 wt. % of ammonium sulphate, followed by solvent extraction of the FMC which is present in the mixture. In this embodiment of isolating FMC a considerable quantity of ammonium salts is formed because of the neutralization of the sulphuric acid used in the Ritter reaction. However, this is an important process because the extraction is particularly complete even using small quantities of extracting agent, which reduces the energy requirement for further working up. In a further reaction step, the 1-formamido-1-methyl-3(4)-cyano cyclohexane (FMC) is then hydrolysed in the acid aqueous medium to give 1-amino-1-methyl-3(4)-cyano cyclohexane (AMC).
A further process variant of DE-A 4,401,929 is to hydrolyze the 1-formamido-1-methyl-3(4)-cyano cyclohexane (FMC), without prior isolation, using the sulphuric acid present in the Ritter reaction mixture.
In all of the process variants described in DE-A 4,401,929 the 1-formamido-1-methyl-3(4)-cyano cyclohexane obtained following hydrolysis is present in an acidic aqueous solution. The isolation of the 1-amino-1-methyl-3(4)-cyano cyclohexane (AMC) by extraction, which follows in the process, can only be carried out from an alkaline solution if it is to be successful industrially. The result of converting the acidic solution to an aqueous solution is that salts are formed as by-products, which must be used or disposed of. The resulting 1-amino-1-methyl-3(4)-cyano cyclohexane (AMC), optionally after separation of the extracting agent by distillation in a known manner, is then hydrogenated catalytically to give 1-amino-1-methyl-3(4)-aminomethyl cyclohexane (AMCA).
The conversion of the acidic aqueous solution of 1-amino-1-methyl-3(4)-cyano cyclohexane to a basic solution is carried out with ammonia in the German publication, which results in the formation of ammonium sulphate and ammonium formate as by-products. It is proposed to thermolytically cleave the ammonium sulphate to form sulphur dioxide, which can be recycled to produce sulphuric acid. Because it is necessary to concentrate the aqueous ammonium sulphate solution before it can be cleaved, this treatment of the by-product salts results in considerable distillation costs.
Treatment of the salt solution for the purpose of recycling ammonium sulphate also results in considerable costs because the ammonium sulphate solution obtained has a chemical oxygen demand (COD) of 10 g per liter even after the extracting agent contained in the salt solution has been removed by distillation and the formate has been removed.
In the catalytic hydrogenation of 1-amino-1-methyl-3(4)-cyano cyclohexane (AMC) to 1-amino-1-methyl-3(4)-aminomethyl cyclohexane (AMCA), which is disclosed in the German publication, intramolecular cyclization and intermolecular dimerization processes result in by-products I, II, III, IV and V. ##STR2## These by-products are present in an amount of approximately 20%. In other words there is a loss of selectivity of approximately 20%.
It is an object of the present invention to provide a process for the preparation of 1-amino-1-methyl-3(4)-aminomethyl cyclohexane (AMCA), which has a markedly higher total selectivity (based on the 4(5)-cyano-1-methyl cyclohexene (CMC) starting material) and in which the ammonium sulphate-containing effluent, which is obtained as an unavoidable by-product, can be worked up economically to give recyclable ammonium sulphate.
This object can be achieved with the process according to the present invention, which is described hereinafter.